Liu, ChengYang, YiLiu, XinDing, YongArain, ZulqarnainLi, XinyeLi, YuanlongZhou, ZianDai, SongyuanNazeeruddin, Mohammad Khaja2021-06-082021-06-082021-06-082020-05-2810.1039/d0ta02807jhttps://infoscience.epfl.ch/handle/20.500.14299/178760WOS:000539350100011All-inorganic cesium lead iodide perovskites (CsPbI3) are promising materials for efficient solar cells. However, they suffer from the formation of an undesired yellow delta -phase under ambient conditions. Herein, we provide a novel strategy to in situ prepare quasi-quantum dot (QQD) CsPbI3 films by using a new ligand, adamantan-1-yl methanammonium (AMDA), with ultralow contents (similar to 0.25 wt%) in the perovskite films. Strong interaction and charge coupling between the ligands and nanocrystals significantly increase the surface Gibbs energy of CsPbI3 and suppresses the grain sizes to around 30 nm, which effectively protects the black alpha -phase from the destruction of moisture and heat. By reducing the trap density of states in the QQD CsPbI3 films, the all-inorganic PSCs exhibit a power conversion efficiency of 13.5%. Most importantly, the QQD CsPbI3 films can substantially maintain an alpha -phase and the QQD-based PSCs retain 90% of their initial efficiency after storage either under ambient conditions for 30 days or 85 degrees C heating for 336 h. These results indicate that in situ prepared QQD films are a potential strategy to effectively improve the long-term stability of all inorganic perovskite materials.text::journal::journal article::research article